This link gives information in that regard. He seems to go back and forth, that is to say, he’ll say something that comes across as pro-choice, and then he quickly backs off of it.
https://www.lifesitenews.com/news/ben-carson-confusion
You don’t get those types of reactions from Santorum, Huckabee, or Jindal, though. At least I’ve never heard them stray from 100% pro-life [over the years], yet they are sitting at the bottom of the polls. :(